DE 10 2008 038 351 A1 discloses a power plant with a heat pump. A working medium is vaporized in a boiler, whereupon it drives a turbine. Then, the working medium is first cooled by means of a heat pump, then supplied to a pump and finally once again heated by the heat pump before it once again reaches the boiler.
DE 30 34 500 A1 describes a heat pump without a compressor, to be installed in a steam power plant.
U.S. Pat. No. 2 982 864 A relates to a heat circuit for a power plant, using the thermal energy produced therein.
Even today, electrical energy is largely generated by means of thermal power stations. Such thermal power stations use fuels such as coal, natural gas, biogas, oil, wood or wood products. Such thermal power stations may operate according to a thermodynamic Clausius-Rankine cycle. In that context, a working medium, for example water, is heated such that it transitions from a liquid state to a gaseous state and thus drives a turbine. Since the working medium is still at a relatively high temperature at the turbine outlet, it must first be cooled and condensed before it can again be heated and vaporized in the cycle. If the heat extracted during the cooling process is given off to the environment, this power plant has a relatively poor degree of utilization.
In order to increase the efficiency of the system as a whole, therefore, the heat present at the turbine outlet is in addition used for heating purposes. The consumers in the heat circuit thus support the cooling of the working medium such that, on one hand, less energy need be given off unused to the environment and, on the other hand, the additional energy requirement for cooling the working medium in the power plant can be reduced. For that reason, such a cogeneration power plant is markedly more efficient than a power plant which serves exclusively for the generation of electrical energy.
In the case of relatively high outward-flow temperatures in the heating circuit, the return-flow temperatures in the heating circuit can still be high enough that the working medium has to be additionally cooled before the working medium can again be used for steam generation. On one hand, this additional cooling requires the use of extra energy and, on the other hand, the remaining heat energy of the carrier medium is lost, unused.
Moreover, there is normally a need for heat on the consumer side of the heating circuit, which need only very seldom corresponds to the quantity of heat which is produced when generating electrical energy. In the majority of cases, the quantity of heat from generating electrical energy differs substantially over time from the quantity of heat which is required by the thermal consumers of the heat circuit.
If, in the case of relatively high demand for electrical energy, only a relatively small quantity of heat is removed by the consumers, the additional excess thermal energy has to be given off unused to the environment while using further energy for the cooling process. If, conversely, the demand for heat on the side of the thermal consumers in the heating circuit is greater than the quantity of heat which can be provided by generating electrical energy, the demand for heat cannot be satisfied and additional heat energy has to be provided by other means and fed into the heating circuit.
There is therefore a need for a cogeneration power plant in which also the residual thermal energy from the return of the heating circuit can be used as efficiently as possible.
There is furthermore a need for a cogeneration power plant in which the outward flow of the heating circuit can always be supplied with a sufficient quantity of thermal energy.
Moreover, there is also a need for a cogeneration power plant with higher overall efficiency.